Production of aromatics



Patented Apn 1949 PRODUCTION OF AnoMA'rIos Everett Gorin, Dallas, re'a, andJohn a. Vorwerck, Maplewood, La., assignors, by mesne sissignments, to Socony-Vacuum Oil Company,

' Incorporated, of New York New York, N. Y., a corporation No Drawing. Application March 2, 194 5, T I

Serial No. 580,7 1'6 is Claims. 101. 260 473) This invention relates to the pyrolysisof methane or natural gas for the production of aromatic hydrocarbons. This application is a continuation in part of our copending application, Serial No. 399,942, filed June 26, 1941, now abandoned, and is concerned particularly with the production of benzene from methane.

The formation of benzene by the pyrolysis of I We have also found that ii we operate our pronormally gaseous hydrocarbons such as methane,

ethane and propane, is'known. However, for

example, in the strictly thermal conversion of methane to benzene, the benzene only becomes quantitatively measurable at temperatures above about 900 C. By increasing the temperature 1 the yield will show a gradual rise up to 6-10% at l 0-- l300 C., and then it begins to fall oi as the reaction temperature is raised still higher.

7 Numerous attempts have been made to discover catalysts or other means for aiding the pyrolysis of methane to benzene in order that lower reaction temperatures may be used and the yield 1 of benzene increased. These attempts have been rather uniformly unsuccessful.

, It, therefore, is an object of" our invention'toprovide an improved process of converting normally gaseous hydrocarbons ,such as methane or a dry natural'gas to light aromatic hydrocar- Another object is to afford a process of f bons. converting methane to aromatic hydrocarbons which is an improvement over strictly thermal processes-for accomplishing such a conversion.

Another object is to afiord an improved-process of converting a dry natural gas, substantially free cess at temperatures substantially above 1000 C. .the reactiontends to produce unsaturated; aliphatic hydrocarbons such as acetylene and ethylene. Hence we prefer to operate our process at temperatures below 1000C. to produce, benzene and homologs of benzene.

The chlorine or bromine used in our process may be designated a reaction promot'er'rather than a catalyst since the halogen is chemically .bound during the reaction to form a hydrogerif halide. As a result we obtain the very desirable thermal advantage'ma'de' possible by the high exothermal reaction-of the halogen to form the hydrogen halide. 'Thus', in the prior artf the pyrolysis reactions are highly endothermic, 'requiring a large heat input at a very-high temper ature level, i. e., above 1000 C. Such a requirement,-obviously, imposes a considerable complexity of apparatus and technique on these prior I methods.- On the contrary, if the principles of ourinvention are followed so that a large amount of chlorine or bromine is used as a reagent, and contact times are employed which result in substantially all the chlorine. and bromine being a converted to the hydrogen halide, then the overof condensible hydrocarbons to light aromatics at temperatures below 1000 C. A more specific object is to provide a process of converting methane to benzene in substantial amounts at temperatures below 1000 C. These and other objects will be apparent our invention.

We have round that by carrying but the pyrolysis of methane in the presence of relatively large amounts of free chlorine or free bromine from the description of and for a sufiicient length of time to convert at least a predominant portion of the chlorine or bromine to the corresponding hydrogen halide all reaction is exothermic. The operating and economical advantages afforded by this latter type process are readily apparent.

Therefore, one of the outstanding features of our invention is the provision of a process of converting methane to benzene that is not endothermic. This fact is strikingly illustrated by the following comparison of the heat requirement of our process with a strictly thermal R Another very important aspect ofthis invention is that it permits the production of benzene from methane at temperatures below 1000 C. The process may be operated at temperatures state we may employ temperatures below 1000- C. and the overall operation is thermoneutral or even exothermic, the pyrolysis in the presence of a large amount of chlorine or bromine wecbtain at any given temperature a substantially increased. yield over that obtained at the same temperature in a strictly thermal process, or we can use a substantially lower temperature to obtain the same yield.

Further, by carrying out up to 1200 C. as in the thermal process. However, as' stated hereinabove, the tendency to obtain less yield of aromatics and higher yields of acetylene increases if temperatures above 1000 C. are used, especially if relatively short contact times are employed We prefer toemploy contact times of 'from about three seconds to sixty seconds.

The contact time as used herein is expressed as the volume of reaction space divided by the average rate of flow of gas at standard conditions the reaction zone.

removed.

of temperature and pressure through the reactor,

that is, the reciprocal of space velocity; The actual residence time is considerably shorter than this and may be determined from the contact time by. multiplying by the factor where T is the temperature in degrees Kelvin in The amount of chlorine or bromine reagent The temperature of operation'should be above about 700 0. Thus, in our preferred operation weemploy temperatures between about 700 C. and 1000' C. It'is not necessary to maintain uniform temperature throughout the conversion zone for the successful operation of our process.

Thus, the chlorine and methane mixture maybereacted initially for short contact times at temperatures in the neighborhood 'of 1000? C., and

the-productgases then allowed to cool gradually f to temperatures of the order of 700 .C.. before. issuing from 'the conversion zone. If desired,

temperatures up to 1200" C. may be used to obtain yields of aromatics greater than obtainable by strictly thermal processes in the absence of low 1000'C, Thus, for example, a comparative .vention.

without; departing from thescope of the inl ramplel' A methane-bromine mixture, containing 17% by volume of bromine was pyrolised at 925' C. for

24 seconds and gave a yield basedontlie methane input of 8.8 mol. per cent of benzene and 8.7 mol per cent of acetylene. Thus. it will be noted that the yield of benzene obtained in this experiment is superior. to that obtained ir'om pure methane alone under. any conditions at a temperature beexperiment made with pure methane alone under the same conditlonlyielded an almost negligible conversion to benzene.

Example 1 A methane-bromlnefmixture, containing 21% by volume of bromine was pyrolized at- 775' C. with a contact time of 52 seconds. Based on the methane input, a yield of 4.7 mol-per cent benzene, 1.8 mol per cent acetylene and 3.4 mol per. cent of ethylene was obtained. The bromine was completely consumed to produce hydrogen bromide;

Example I!! Y 1 A methane-bromine mixture, containing 20 by-volume of bromine was pyr lized at 1000' C. with 'a contact time of 11.8 seconds. operation gave a yield in moi per cent, based on the methane input, of 11.0 per cent per cent acetylene.

. Esample IV "A -methane-chlorine mixture containing 31% by volume of chlorine was 'pyrolized at 825' C. with a contact .time of 23 seconds. 'Based on the promoters, although in the upper temperature range the tendency to form. unsaturated ali phatics is increased. The preferred range of contact times above refer to the total time of contact of the gas mixture in the whole conversion zone.

The operating procedure for our process may be substantially the same as that known to those skilled in the art for thermally converting methane to benzene. Thus, the methane, after removal of sulfur, if necessary or desired, may have the proper amount of halogen reagent added to it and the mixture is then passed at conversion temperatures through a conventional converter. Liquid bromine may be supplied to the gaseous hydrocarbon reactant by bubbling the latter through the bromine to incorporate therein the gaseous bromine volume content within the above limits or chlorine may be added directly as a gas to the hydrocarbon gas. It is to be understood, however, that the halogen reagent may be introduced in any other suitable manner. For example, because of the highly exothermic nature 'of'the reaction caused by the halogen it may be desirable to introduce this reagent at a plurality of points along the converter in order to obtain better heat distribution 5 and hence improved temperature control. F'urther, it is to be understood that the total yield of benzene may be increased by further pyrolysis of product gases from which benzene has been In order that the invention may be illustrated more fully, the following speciflcexamples are given. It is to be understood that the process is not limited to the specific details of these ex-,

amples, as there maybe variations therefrom methane input, a yield of 11.3 mol per cent benzene and 4.2 mol per cent of acetylene was ob- I tained. Thus, it is seen,that an increase in the amount of halogen increases the relative amount of benzene with respect. to acetylene produced.

In a comparative operation under the same conditions except that no reaction promoter was used, the yield of benzene and other useful products was negligible. I

Example V V Methane and chlorine were mixed in the ratio of. 65 parts'by volume of methane to 35 parts by volume of chlorine, and the mixture was passed at a c. ltact time of 0.045 second through a quartz 'reaction tube maintained at1020 C. After removal of the hydrogen chloride the eiliuent gas had the following composition: C2-C5 'un'satu rated gases, that is, acetylene, ethylene. butadiene, vinyl acetylene, etc.,- 10.0 vol. per cent, 0.8 vol. per cent of Cpl-polymers, 3.2'vol. per cent hydrogen, 14.7 volper cent methyl chloride, 3.5 vol. per cent methylene chloride and the remainder unconverted methane. The Cs-i-polymers consisted of highly unsaturated materials such as divinyl acetylene and contained little or no benzene. The total conversion of methane to higher hydrocarbons amounted to 27.0% of the methane passed. This operation illustrates the inadequacy of short contact times inthe production of benzene with chlorin'e as a reagent.

' Example VI .A mixture containing 33 mol per cent of chlorine and 67 mol per cent of methane was pyrolized at 960 C. and a contact time of 0.3 second. The

' eiiluent gas after removal of hydrogen chloride contained 6.4% acetylene but no benzene, .thus

benzene and 7.8

illustrating again the necessity for adequate contact time in our process for producing benzene from methane.

Some methyl chloride is always'formed as an intermediate and a small amount may remain in the eflluent gas particularly when temperatures below 800 C. are employed. It is generally desirable to recycle the total eiiluent gas to the pyrolysis zone after removal of the hydrogen chloride and aromatic products. Under these conditions any methyl chloride present is further pyrolized to produce hydrogen chloride and aromatic hydrocarbons. By such a recycling procedure an ultimate yield of 60% of aromatic hydrocarbons boiling in the gasoline range may be obtained while the remainder of the methane is converted to aromatic tars and carbon. The regeneration of the free halogen acid-,by-product 6. The process of manufacturing normally liquid aromatic compounds from a hydrocarbon gas containing a minimum or 90 per cent of methane plus C: hydrocarbons which process comprises pyrolizing a mixture of from 85 parts by volume to 60 parts by volume or said methane and C2 hydrocarbon containing gas with from parts by volume to 40 parts by volume of a halogen selected from the class consisting of chlorine and ogen within the range from 3 seconds'to' 60- secmay be accomplished in any suitable manner substantial part of the propane from a wet natural I gas. Such a dry natural gas will usually contain a minimum of 95 vol. per cent of methane plus C: hydrocarbons. The methane plus C2 hydrocarbon content of residue dry gas obtained from very "we natural gas by removal of condensables, including with condensables a substantial part of the propane content of the wet gas, may be as low as 90 vol. per cent. Our invention should be construed to include such a residue gas as being within the definition of a dry natural gas.

We claim:

1. The process of converting a dry natural gas to liquid aromatic hydrocarbons which comprises pyrolizing a mixture consisting essentially of from 85 tov 60 parts by volume of said natural gas with onds so that substantially all of the said halogen is converted to hydrogen halide.

7. The process of claim 6 wherein the hydrocarbon gas is a natural gas from which the major part of C: hydrocarbons and substantially all of the hydrocarbons having more than three carbon atoms per molecule have been removed.

8. The process of claim 6 wherein the halogen is chlorine.

9/The process of claim is bromine.

10. The process of manufacturing benzene from methane which comprises pyrolizlng a mixture consisting essentially of from 85 to '10 parts by volume of methane with from 15-to 30 parts by volume of a halogen from the group consisting of chlorine and bromine at'a temperature above 700 C. but not exceeding 1000",C. and regulating the contact time of the reactants within the range of from 3 to 60 seconds so that substantially all or said halogen is converted to the hydrogen halide.

11. The process of claim 10 wherein the halogen is chlorine.

more than two carbon atoms per molecule which 1 comprises pyrolizlng a mixture consisting of from from 15 to 40 parts by volume of a halogen selected from the class consisting of chlorine and bromine at a temperature within the rangeof from about 700 C. to about 1000 C. and regulating the contact time so that substantially. all of said halogen is converted to the hydrogen halide.

2. The process of converting methane to benzene which comprises pyrolizing a mixture consisting essentially of from 85 to 60 parts by volume of methane with from 15 to 40 parts by volume oil a halogen selected from the group consisting of chlorine and bromine at a temperature within within the range of'800 C. to 1000 C. for a period 01' time within the range of from about 3 seconds to about fiiiseconds.

85 to parts by volume oi said natural gas based on the hydrocarbons therein with from 15 to 30 parts by volume of a halogen selected from the group consisting of chlorine and bromine at a temperature above 800 C. but not exceeding 1000 c. and regulating the contact time 6: the

reactants within the range or from 3 to 60 seconds so that substantially all of said halogen is is chlorine. 7

.JOHNRVORWERCK.

r nnrnnencnsfcrrnn The following references are of: record in the tile 01' thispatent: I 1

UNITED STATES PATENTQ Number Name Date 2,004,072 Haas et al. June 4, 1935 2,221,658 Waterman et ai. Nov. 12, 1940 2,334,033

OTHERCES 70 6'13 (pages 323-7).

6 wherein halogen Riblett Nov. 9, 194a 

